Asked  7 Months ago    Answers:  5   Viewed   37 times

I'm looking for a simple way to create an array in php that will not allow duplicate entries, but allows for easy combining of other sets or arrays.

I'm mostly interested in whether such a feature exists in the language because writing my own wouldn't be difficult. I just don't want to if I don't need to.



Just an idea, if you use the array keys instead of values, you'll be sure there are no duplicates, also this allows for easy merging of two "sets".

$set1 = array ('a' => 1, 'b' => 1, );
$set2 = array ('b' => 1, 'c' => 1, );
$union = $set1 + $set2;
Wednesday, March 31, 2021
answered 7 Months ago

**Solution! Actually I solved this problem by changing the code slightly. I was writing the row and column headers first and then adding the inner table values after. I changed it so that I added the headers and data as I incremented through the rows and columns as shown in code below. Might help someone else.

$query_ctry = mysql_query("SELECT DISTINCT country FROM totalslist ORDER BY country");
$numctry = mysql_num_rows($query_ctry);
$query_company = mysql_query("SELECT DISTINCT entity FROM totalslist ORDER BY entity");
$numcomp = mysql_num_rows($query_company);

while($srow = mysql_fetch_assoc($query_company))
    $newarray[] = $srow['entity'];
$row3 = 2;
$col3 = 1;
while($trow = mysql_fetch_row($query_ctry))
    $country = $trow[0];

    while($comp = each($newarray))
        $company = $comp[1];
        $total = mysql_query("SELECT noparts FROM totalslist WHERE country = '$country' AND entity = '$company'");
    if ($numrows = mysql_num_rows($total) == 0)
        $totalres = 0;
        $result3 = mysql_fetch_row($total);
        $totalres = $result3[0];
    $objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow(0, $row3, $country);
    $objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow($col3, 1, $company);
    $objPHPExcel->getActiveSheet()->setCellValueByColumnAndRow($col3, $row3, $totalres); 

        $col3 = 1;
        // Save Excel file
        $objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
Wednesday, March 31, 2021
answered 7 Months ago

In PHP 7, if you iterate an array by value, the copy will be done lazily, only when and if the array is actually modified.

If you iterate an array by reference instead, a separation will be performed at the start of the loop. If the array is currently used in more than one place, this separation will lead to a copy.

Furthermore iterating by reference means that a) the array has to be wrapped into a reference and b) each element has to be wrapped in a reference as well. Creating a reference wrapper is an expensive operation, because it requires allocation.

Additionally iteration by reference requires us to use a modification-safe iteration mechanism. This works by registering the iterator with the array and checking for potentially affected iterators in various array modification operations.

So no, iterating by reference is certainly not an optimization, it's a de-optimization. Using references usually is.

Wednesday, March 31, 2021
answered 7 Months ago

When you set cell values individually, you have the option of setting the datatype explicitly, but when you use the fromArray() method, you don't have this option.

However, by default, PHP uses a default value binder to identify datatypes from the values passed, and set the cell datatype accordingly. This default behaviour is defined in a class /PHPExcel/Cell/DefaultValueBinder.php.

So you can create your own value binder, as described in the PHPExcel Documentation, that would set every value as a string datatype.

Something like:

class PHPExcel_Cell_MyColumnValueBinder extends PHPExcel_Cell_DefaultValueBinder implements PHPExcel_Cell_IValueBinder
    protected $stringColumns = [];

    public function __construct(array $stringColumnList = []) {
        // Accept a list of columns that will always be set as strings
        $this->stringColumns = $stringColumnList;

    public function bindValue(PHPExcel_Cell $cell, $value = null)
        // If the cell is one of our columns to set as a string...
        if (in_array($cell->getColumn(), $this->stringColumns)) {
            // ... then we cast it to a string and explicitly set it as a string
            $cell->setValueExplicit((string) $value, PHPExcel_Cell_DataType::TYPE_STRING);
            return true;
        // Otherwise, use the default behaviour
        return parent::bindValue($cell, $value);

// Instantiate our custom binder, with a list of columns, and tell PHPExcel to use it
PHPExcel_Cell::setValueBinder(new PHPExcel_Cell_MyColumnValueBinder(['A', 'B', 'C', 'E', 'F']));

$objPHPExcel = new PHPExcel();
Friday, May 28, 2021
answered 5 Months ago

There's no special reason, to my knowledge - I'd guess that the reason is that for so many applications the highly-tuned dict and set implementations (which are hash tables) work well. They're good enough in most cases. There are definitely situations where you need the performance characteristics of balanced binary search trees (like ordered traversal based on key- rather than addition-order), but those are far enough off the beaten path that people are happy with grabbing a third-party package in that case.

I've had a good experience using the bintrees package on PyPI. This has implementations of unbalanced, AVL and red-black binary trees, in both pure Python and as extensions written in Cython.

I think the rest of the reason is essentially historical accident. If the person who wrote bintrees lobbied for its inclusion in the stdlib, and was willing to put up with the constraints that imposes on maintenance and releases, it would probably go in. (Although the Cython dependency would cause a problem, I'd guess.)

Algorithmic complexity:

For hash tables (like dicts or sets), insertion and lookup are O(1), while for a balanced tree these are O(log(n)). In-order traversal of keys is O(n) in a tree, but to do the same thing with a hash table you need to sort the keys first, so it's O(n*log(n)). When you're picking which kind of data structure to use, you need to think about which operations you're going to be using, and pick the tradeoff that makes the most sense in your application.

Monday, August 9, 2021
answered 3 Months ago
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